1. Field of the Invention
The present invention relates to a tool that enables centering of a drill bit to accurately center a hole after an initial countersink has been bored in the workpiece. The fields most likely to benefit from this invention are the construction and home building trades. However, the beneficial aspects of the invention may also be utilized in other fields such as the machine tool industry.
Thus it can be seen that the potential fields of use for this invention are myriad and the particular preferred embodiment described herein is in no way meant to limit the use of the invention to the particular field chosen for exposition of the details of the invention.
A comprehensive listing of all the possible fields to which this invention may be applied is limited only by the imagination and is therefore not provided herein. Some of the more obvious applications are mentioned herein in the interest of providing a full and complete disclosure of the unique properties of this previously unknown general purpose article of manufacture. It is to be understood from the outset that the scope of this invention is not limited to these fields or to the specific examples of potential uses presented hereinafter.
2. Description of the Prior Art
It has long been difficult to accurately center a drill hole in an existing countersink in a workpiece. In prior drill bit centering devices it has been difficult to drill accurately in various materials. In special uses additional tools such as chisels to align the drill bit after an initial countersink has been bored, are required.
Prior art drill guides were often of considerable length due to the construction of an extendible and retractable guide member. This demanded the use of twist drills or cutting tools of considerably greater length than was actually required for the drilling operation. These greater lengths often exceeded the ordinary standard drill lengths for given diameters of drills.
One technique, used in the past, was to almost completely enclose the entire length of a centering device for drill bits. The result was that only minimum space was available for escape of cuttings, shavings and chips generated from the drilling.
A self-centering bit is described in U.S. Pat. No. 2,792,726 issued to Selmer E. Vick on May 21, 1957. The Vick patent discloses an outer barrel with an enclosed spring and two holes or slots in a barrel surrounding the bit. This permits limited escape of any shavings which follow or flow up the bit into a sleeve. By contrast, the instant invention has an open spring between a locking collar and a centering cone which surrounds the exterior of a drill bit, allowing an enlarged discharge area for shavings from the drilling.
The bit centering device in U.S. Pat. No. 2,224,480 issued to Joseph Kartarik on Dec. 10, 1940 shows a spring between a threaded cap and slidable section. Intermediate sections are provided with openings to permit the escape of drilling scraps outwardly. A contrast with the instant invention is that the intermediate section is substantially open between the locking collar and centering cone between the turns of the enclosing spring.
In U.S. Pat. No. 2,479,774 issued to Clyde A. Pierce on Aug. 23, 1949, discloses a drill bit centering attachment having holes to allow shavings to escape. By contrast the instant invention has an expanded discharge area between the locking collar and centering cone.
U.S. Pat. No. 2,335,614 issued to Louis A. Spievek on Nov. 30, 1943 shows a counterbore and a laterally extending opening in the side of a pressure foot providing ejection space for cuttings or chips. In contradistinction, the instant invention is a one piece shank and drill bit combined with screw thread type projections for the opposite ends of the spring between its locking collar and centering cone.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. As will be seen, the simplicity and effectiveness of my invention is not rivaled in the prior art.